The valences of manganese and vanadium oxides in multi-layer ceramic capacitors (MLCCs), sintered under a reducing atmosphere, were investigated using electron paramagnetic resonance; insulation resistance degradation was analyzed using impedance spectroscopy in highly accelerated lifetime tests to clarify the influences of manganese and vanadium on both the electrical properties and microstructure of MLCCs. The Mn(2+) was stable in the reducing-atmospheresintered MLCCs and formed a grain boundary. Vanadium mitigated insulation resistance degradation and increased the reliability of the MLCCs. Although V4+ was detected in MLCCs that had 0.20 mol% and 0.30 mol% of added vanadium, the electrical properties were dependent upon other ions, e.g., V(3+) or V(5+). All vanadium ions except for V(4+) decreased the insulation resistance of ceramic/electrode interface. This is because vanadium reduces electric field concentration at the ceramic/ electrode interface and delays the onset of oxygen vacancy migration in the early stages of a highly accelerated lifetime test.
The valence of vanadium was measured by electron paramagnetic resonance in order to explain the decrease in insulation resistance (IR) and the improvement in highly accelerated lifetime that resulted from the addition of vanadium. V4+ was detected in specimens with vanadium contents of 0.20 and 0.30 mol %, while no V4+ was detected in a specimen with a vanadium content of 0.06 mol %. It was also revealed that the content of the vanadium except for V4+ are the main factor responsible for the decrease in IR and the improvement in lifetime. The impedance of BaTiO3-based materials in multilayer ceramic capacitors with various vanadium contents was investigated in order to determine the mechanism of improving the highly accelerated lifetime using a four resistance and capacitor section electrical equivalent circuit. All four resistance components (R components) decreased with an increase in vanadium content. During the lifetime test, all four R components were degraded. In particular, the R component corresponding to the ceramic/internal electrode interface regions was more strongly degraded than the other three R components, and it was found that this component was the main factor responsible for the degradation of IR during the test. The resistance degradation of this component tended to occur slowly when the vanadium content increased, which resulted in the improvement in lifetime. The primary part of this degradation was implied to be controlled by diffusion.
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